Electromagnetic induction pump for molten metals



Jan. 2, 1951 M. TAMA ELECTROMAGNETIC INDUCTIOfi PUMP FOR MOLTEN METALS Filed Feb. 15, 4946 3 Sheets-Sheet l INVENTOR. f

Jan. 2, 19.51

' 3 Sheets-Sheet 2 Filed Feb. 15,- 1946 INVENIQR M3 PM ATTORNEY Jan. 2, 1951 M, T M 2,536,325

ELECTROIAGNETIC INDUCTION FUN? FOR IIOLTEN IIETALS Filed Feb. 15, 1946 3 Sheets-Sheet 3 INVEJATOR 140'! lm BY M ATTORNEY .metals, for instance:

Patented Jan. 2, 1951 ELECTROMAGNETIC INDUCTION PUMP FOR MOL'IEN METALS Mario Tama, Morrisville, Pm, assignor to Ajax Engineering Corporation, Trenton, N. J.

Application February 15, 1946, Serial No. 647,831

6 Claims.

This invention relates to a device for the transport of molten metals at high temperatures by means of electro-inductive forces; this device will be called in the following an "electromagnetic induction pump ,for molten metals" of the type which is also described in copending later filed patent applications Ser. No. 671,818, filed May 23, 1946; Ser. No. 683,115, filed July 12. 1946, and Ser. No. 735,851, filed March 20, 1947.

His the main purpose of this invention to transport molten metals, for instance aluminum, copper, zinc and their alloys against gravity through a tube which freely reaches into a melting channel of an induction furnace by the sole use of electromagnetic forces.

The realization of this purpose opens a variety of useful methods for handling molten 1) The discharge of the molten metal from a stationary melting furnace and the elimination of tilting or ladling equipment.

(2) The transfer of the molten metal from .one container into a second container, for instance, from one furnace chamber into a second furnace chamber and the reversal-of the current in order to obtain circulation in the opposite direction,

(3) The syphoning of metal from one container to another, g

(4) The starting of a syphon for the molten metal, I

(5) The tapping or spigoting .of the molten metal from a furnace into permanent or diecasting molds,

(6) The jerk-free uniform discharge of molten metals from a submerged resistor type induction furnace by pumping.

Another object of the invention is to control the pumping speed by regulation of the current intensity. 7

It is also an object of the invention to provide means for an easy starting and stopping of the flow of the molten metal through a pipe line.

The physical laws providing the basis for this invention are the following.

when an electric current is forced to pass through a conductormolten or solidit, creates a magnetic field within the conductor and outside of it. Only the field within the conductor produces forces beneficial for carrying out the invention.

ductor and the magnetic field elements cutting through said current elements internal forces are created within the conductor.

If the conductor is a molten metal, electromagnetic pressure gradients are established within the conductor with zones of high pressure at certain places and zones of low pressure at other places. The forces are directed towards the center of the magnetic field and the direction of the forces can be determined by the wellknown three-finger rule. If alternating current is used the direction of the forces is not changed when the current is reversed. Therefore, the pressure gradients created within the-molten metal are always maintained in a definite direction during the entire process.

An evaluation of the forces produced by virtue of the aforementioned principles has been recited in U. S. Patents Nos. 2,375,049 and 2,381,523.

The first physical explanation of the pressures and forces in liquid electric conductors was given by Dr. E. F. Northrup in an article published in "Physical Review, 1907, page 474 and following. These forces have been collectively known as the "pinch effect" and many industrial uses thereof have been suggested in the past. However, no practical utilization of this principle a for the pumping and discharging of molten metals having a high melting point. has been made heretofore in spite of its apparent advantages.

The distribution of the liquid pressures createdin the interior of molten conductors by induction is not easy to evaluate in a general way. But a good approximation can be obtained by examining the conditions existing in a long conductor of circular cross section carrying a heavy current with the return conductor at a-considerable distance away, in which case the center of the magnetic field coincides with .the geometric center of the circle.

The liquid pressures caused by the current fiow ing through a circular conductor are zero at the periphery and reach the maximum value at the center line; they are, as generally known, propagated in all directions; their distribution is symbolica'lly illustrated in Fig. 1 of the attached drawings, where the liquid pressures for each point within a circle m having a radius 1' may be entered as vertical arrows on the plane of this circle; it is, however, well understood that this manner of illustration is not intended to indicate that the pressures are all in the same direction. The arrow P, for instance, signifies the pressure Where Pm=liquid pressure at center line in dyn./cm. J=current density in amperes cm. r==radius of the conductor in cm.

The value of the pressure at any intermediate points X within the plane of circle m located at a radial distance a: is

with the same dimensions as in Equation 1.

In carrying out the present invention, however, it has been found that practical pumping and metal discharging efficiency cannot be obtained if only the maximum pressure is used. Larger amounts of metal can be transported if a large part or the entire cross section of the conductor is utilized for pumping purposes.

In order to evaluate the pressures obtainable under such conditions the average pressure over the entire cross section of circle m must be computed. The same purpose is achieved by determining the height of a cylinder having the same volume and the same radius as the paraboloid Z. By integration it is found that the average pressure Par is equal to one-half of the maximum pres.ure:

The values thus deducted from the physical laws check approximately with practical measurements obtained with the instant method.

In the straight circular channels preferably used in connection with the hereafter described pumping and discharging device the magnetic fleld is frequently unsymmetric; hence, the center of the magnetic field lines will be located outside of the geometric center of the circle; in these cases the maximum of pressure will be found in an excentric location relative to the center of the magnetic field.

The utilization of electromagnetic or repulsion forces between the primary and secondary for the pumping of liquid conductors is generally known. However, in these prior art devices, the electromagnetic moving impetus is directly applied to the liquid by magnets or metallic electrodes or conductors and the horizontally extending passage for the liquid conductor is being recessed from a metal plate. Based on the. same principle of direct current connection, tubes have been designed to transport liquid conductors in a horizontal direction, the tube walls being provided with slots and the current being passed by metal electrodes through the slots to the fiui conductor.

In all these prior art devices the path of the current is perpendicular to the flow direction of the liquid conductor and specially shaped magnets are provided to serve this end.

Many attempts have also been made to utilize the repulsion effect between the primary and the secondary for the movement and the circulation of molten metals in induction furnaces.

. v In the August issue, 1922, of The Metal Industry"the circulation of molten metal is described through the channels of the melting loop of an induction furnace by the axial displacement of the primary relative to the secondary. A similar metal movement is shown in Belgian Patent 459,551. It has also been suggested to upwardly transport molten metal contained in a pot by inductive forces; here the metal is maintained in the molten state by the outside action of a flow of heating gases. None of these suggestions has attained the status of ,practical usefulness.

The invention signifies a decided departure from the art; it is based on the discovery that an entirely diflerent and more effective utilization of the magnetic field had to be found which renders it possible to operate with high pressure differences within the molten metal and not with the natural forces created by the magnetic field in combination with the use of electrodes or magnets.

The invention therefore utilizes the liquid pressures illustrated in Fig. 1 of the drawings, thereby creating a flow of the molten metal in the same direction as the current flows which is a principal deviation from the prior art, where the pumping of the liquid conductor results from field lines cutting the same transversaily to its flow direction.

According to the above referred-to Equations 1 and 2 the internal pressures increase with the square of the current density; hence, with large current densities appreciable pressures may be obtained and forces created which are of particular importance for the discharge of molten metals by pumping.

As stated before, an important object of this invention is the jerk and eddy-free uniform transport and discharge of molten metal from an induction furnace by pumping. The molten metal charge is, as generally known, in a submerged resistor type induction furnace in a state of violent motion caused by the induced electromagnetic pressures.

The influence of these pressures in the melting section of a submerged resistor type induction furnace is illustrated in Fig. 2 of the attached drawings which represents the current influenced secondary hearth loop and the lower part of the metal holding hearth, denoted in this specification as a "current influenced restricted" section of the bath.

The electromagnetic field of highest intensity is located in the center portion of the straight channels l5, II at about half their length. The metal is forced from this center section in an upward and in a downward direction through the melting channels as indicated by the arrows. The molten metal stream emerging from the upper and the lower end of the channels draws the metal from adjacent portions of the charge into the same channels, whereby two lateral flow branches result which are again upwardly forced as they approach the center portion of the channels. Under the direct influence of the electromagnetic field an intensive up-and-down flow of the melt through the same channel results.

Naturally, these adjacent up-and-down streams of the molten metal do not pass each other as smoothly as illustrated in the drawing; they actually and continuously collide. The eruption-like agitation of the metal is the consequence of these collisions.

Within the range of its highest intensity the electromagnetic field has the tendency to compress the molten conductor; if the current input is sumciently high, it may happen that the conductor is interrupted or pinched: thus the term pinch effect was created.

. However, and as above stated, the direct return of the metal into the same melting channel is the consequence of the metal pressure produced by the electromagnetic field and the resultin sucking effect-in coacti'on with the pressure distribution in these sections of the molten charge;

it will not take place in those portions or layers pressures inherent in the bath for its transport and discharge from the furnace as it seemed impossible that means could be provided which assasao I carried out in a furnace as above described where would render a jerk and eddy-free uniform outflow of the metal possible which is the main requirement for a successful metal pumping. pouring or casting action.

In spite of the more than forty years notoriety pressures relied upon for the performance of the invention,

Fig. 2 is a vertical section of the lower part of an induction furnace showing the metal movement in the melting zone,

Fig. 3 is a vertical sectional elevation of an electromagnetic induction pump representing a first embodiment of this invention,

Fig. 4 is a vertical sectional elevation taken on lines 4 to 4 of Fig. 3,

Fig. 5 is a vertical sectional elevation of a further embodiment of the invention, and

Fig. 6 is a vertical sectional view taken on line 0 to i of Fig. 5.

Figs. 3 and 4 show the application of the invention to an induction furnace of the type described in Reissue Patent No. 22,602 the invention being used to discharge the molten metal from the furnace.

The current carrying duct system of this pumping device consists of the two outer channels IS, the center channel H, the bottom channel l8, and the groove IS. The two primary coils l9 and 20 induce heavy current in this duct system. The

largest pressure is generated in the center duct or channel H; the pumping tube 2| reaches with its inner end freely into the channel H, The other end of the tube 2| leads to a mold 22; as soon as the pump is set into operation by passing a heavy current through duct this mold is filled with molten metal. by energizing the primary coils l9 and 20 with a voltage to produce sumcient head in tube 2| to overcome the difference in level between the metal bath in the furnace and the mold.

This pumping method has been practically This is accomplished the center duct had a cross section of 50 cm.'; a current of 30,000 amps. was forced through it. The tube 2| had a cross section of 10 cm. and the bath consisting of a molten aluminum alloy was forced out of the pump device into the molds at-a rate of kg./min. overcoming an average difference of level of 15 cm. The flow could be maintained, although at a slower rate, even if the diflerence of level was increased to 32 cm.

with a tube having a cross section of 3 cm. a

flow rate of 40 kgs./min. was obtained under similar conditions.

Another embodiment of the invention is shown in- Figs. 5 and 6 in its application to a furnace which is very similar to that shown in Figs. 3, 4.

The current carrying ducts are the outer channels 24, the center channel 26, the bottom channel 21, and the groove 25. The primary coils are denoted with 28 and 29.

The discharge tube 30 is here arranged somewhat differently; the one end of the tube reaches freely into the current carrying groove which is connected with center channel 26 whereas the other end again leads into mold 3 The diameter of the tubes used for the pumping of the metals may vary within wide limits; it must however besmaller than the current carrying duct. The cross section of the tube determines the amount of metal which is pumped or transported per unit of time. Whereas in the first embodiment of the invention the tube might preferably be a good conductor of electricity this is immaterial with regard to this embodiment.

The current carrying ducts should be lined with a refractory material adapted to withstand the action of the molten metals at the high temperature. The refractory materials which are used for induction furnaces answer this requirement; the metal conveying conduits should be pref erably made of similar refractories.

The method herein described consists of forcing an electric current through a refractory lined duct which contains molten metal and creating thereby a pressure zone, introducing one end of a tube into this pressure zone and leading the other end of the tube to a zone of lower p sure. The molten metal will be accordingly forced to flow from the zone *of high pressure through the tube to the zone of lower pressure, or in other words, it will be pumped from the zone of high pressure into the zone of lower pressure. The pumping force or pressure is exclusively produced by electromagnetic forces which force the molten metal through a tube or pipeline from one place to another.

Essential requirements for the performance of the invention are that an electric current of suflicient magnitude is forced through. the ducts which contain the molten conductor, that the pressure created by the electric current and the magnetic fields originated thereby and cutting through the molten conductor are sufilciently assasaa secondary melting loop to hold a molten metal bath, a transformer assembly to induce current in said secondary melting loop to thereby hold the metal in the molten state and to superimpose in said secondary melting loop an electromagnetic pressure upon the hydraulic bath pressure, a refractory tube freely reaching with its one end into said secondary melting loop and being spaced therefrom, said tube leading upwardly to a, location of reduced electromagnetic pressure whereby a unidirectional flow of the metal is produced .in an upward direction through said tube from the end thereof reaching into the proximity of said secondary melting loop to said location of reduced electromagnetic pressure.

2. In an electromagnetic induction pump according to claim 1 the diameter of the refractory tube being smaller than the diameter of the loop channels.

3. An electromagnetic induction pump for molten metals comprising a receptacle and a secondary melting loop to hold a molten metal bath, a transformer assembly to induce current in said secondary melting loop to thereby hold the metal in the molten state and to superimpose in said secondary melting loop an electromagnetic pressure upon the hydraulic bath pressure, a refractory tube freely reaching with its one end into proximity with said secondary melting loop and being spaced therefrom, said tube leading upwardly to a location of reduced electromagnetic pressure, whereby a unidirectional flow of the metal is produced in an upward direction through said'tube from the end thereof reaching into the proximity of said secondary melting loop to said location of reduced electromagnetic pressure.

4. An electromagnetic induction pump for molten metals comprising a receptacle and a secondary melting loop to hold a molten metal bath. a transformer assembly to induce current in said secondary melting loop to thereby hold the metal in the molten state and to superimpose in said secondary melting loop an electromagnetic pressure upon the hydraulic bath pressure, a refractory current conductive tube freely reaching with its one end into said secondary melting loop and being spaced therefrom, said tube leading upwardly into a location of reduced electromagnetic pressure, whereby a unidirectional flow of the metal is produced in an upward direction through said tube from th end thereof reaching into the proximity of said secondary melting loop to said location of reduced electromagnetic pressure.

5. An electromagnetic induction pump for molten metals comprising a receptacle and a secondary melting loop to hold a molten metal bath, a transformer assembly to induce current in said secondary melting loop to thereby hold the metal in the molten state and to superimpose in said secondary melting loop an electromagnetic pressure upon the hydraulic bath pressure, a refractory current conductive tube freely reaching with its one end into proximity with said secondary melting loop and being spaced therefrom, said tube leading upwardly into a location of reduced electromagnetic pressure, whereby a unidirectional flow of the metal is produced in an upward direction through said tube from the end thereof reaching into the proximity of said secondary melting loop to said location of reduced electromagnetic pressure.

6. An electromagnetic induction pump for molten metals comprising a receptacle and a secondary melting loop composed of a plurality of melting channels to hold a molten metal bath. a transformer assembly to induce current in said secondary melting loop to thereby hold the metal in the molten state and to superimpose in said secondary melting loop an electromagnetic pressure upon the hydraulic bath pressure, a groove in the bottom of said receptacle, a refractory tube freely reaching with its one end into said groove and leading upwardly therefrom into a location of reduced electromagnetic pressure, whereby a unidirectional flow of the metal is produced in an upward direction through said tube from the end thereof reaching into the proximity of said secondary melting loop to said location of reduced electromagnetic pressure.

MARIO TAMA.

REFERENCES CITED The following references are of record in the file of this patent;

UNITED STATES PATENTS Number Name Date Re. 22,602 Tama Feb. 13, 1945 1,595,968 Unger Aug. 10, 1926 1,626,837 Jennings May 3, 1927 1,648,707 Weed Nov. 8, 1927 1,660,407 Bainbridge Feb. 28, 1928 1,792,449 Spencer Feb. 10, 1931 1,953,970 Miller Apr. 10, 1934 2,286,024 Tama et al June 9, 1942 2,339,964 Tama Jan. 25, 1944 2,342,617 Tama et al Feb. 22, 1944 2,368,173 Tama et a1 Jan. '30, 1945 2,375,049 Tama et al May 1, 1945 2,381,523 Tama et al Aug. 7, 1945 2,386,369 Thompson Oct. 9, 1945 2,389,218 Tama et a1 Nov. 20, 1945 FOREIGN PATENTS Number Country Date 126,947 Great Britain 1919 142,110 Great Britain 1920 459,551 Belgium 1945 OTHER REFERENCES Article by Dr. E. F. Northrup in Physical Review, 1907, page 474. I

Iron Age, August 3, 1922, page 271.

The Metal Industry, vol. 20, No. 8, page 312. 

